Sperm navigation along helical paths in 3D chemoattractant landscapes

Area of Science:

• Reproductive biology
• Biophysics
• Cellular dynamics

Background:

• Sperm must navigate complex chemical environments to reach eggs for fertilization.
• Understanding three-dimensional (3D) navigation in chemical landscapes is crucial but remains largely unknown.
• Sperm utilize chemical and physical cues from the egg or oviduct to guide their movement.

Purpose of the Study:

• To investigate the principles of 3D navigation in chemoattractant gradients by sperm.
• To elucidate the mechanisms underlying sperm's directional movement in response to chemical cues.
• To provide a framework for studying microswimmer behavior in complex chemical environments.

Main Methods:

• Holographic microscopy was employed to track sperm movement in 3D.
• Optochemical techniques were utilized to create and manipulate chemoattractant gradients.
• Sperm swimming patterns and responses to chemical stimuli were analyzed.

Main Results:

• Sperm exhibit two distinct timescales of gradient sensing, leading to dual steering responses.
• A periodic component, linked to helical swimming, gradually aligns sperm towards the chemical gradient.
• Sharp turning maneuvers are initiated when incremental path corrections fail, correcting off-course trajectories.

Conclusions:

• Sperm demonstrate sophisticated computational strategies for deterministic klinotaxis in 3D chemical landscapes.
• Turning responses are triggered by a decrease in chemoattractant stimulation, indicated by 'off' Ca(2+) signals.
• The study establishes a conceptual and technical foundation for future research on microswimmer navigation.